It is not long since Paul Bew told Sir George Bain, his ultimate boss as vice-chancellor of Queen's University, Belfast, that he feared being a sought-after commentator on Northern Irish politics might detract from his academic role. Bain told him not to worry: "What use is a professor if he doesn't profess?"

On that measure Bew, professor of Irish politics at Queen's, is as useful as they come. There are few weeks in which his byline is absent from broadsheets on either side of the Irish Sea, or his voice from the BBC, Ireland's RTE or one of the US channels.

He analyses politics as a historian who once talked of the need for "autonomous yet coordinated eyes" - one attuned to the present, the other to the past - and who argues that, for all Ireland's preoccupation with its history, "the important echoes are not always those that are picked up".

He returned to Northern Ireland with a Cambridge degree and doctorate in the mid-1970s, hoping to "apply the Cambridge approach, its rigour and seriousness, to the history of Ireland". That desire has produced a steady stream of publications - many co-written with Henry Patterson, professor of politics at the University of Ulster - covering both Irelands, pre- and post- the 1922 partition, and a weighty commission to write the Oxford History of Ireland since 1789, whose delayed completion was one reason for the unease expressed to Bain. He expects to finish it this year.

Inevitably, the Troubles have defined him personally (coinciding precisely with his adulthood) and professionally. Teaching Irish history and politics at Queen's has the advantage that students need no convincing of the relevance of their studies, but it is unavoidably intense.

To stay in a world that, he readily admits, can be "tense and claustrophic at times", devoted to its often cheerless politics, might seem classic aversion therapy. But he retains the affection for his native province that brought him home in an era when newly minted PhDs had wide options. Any aversion has a single symptom - as a voracious reader of fiction, he says: "I cannot bring myself to read novels set in Northern Ireland, particularly those of the 20th century", although he accepts he will need to overcome his revulsion for the sake of the Oxford History.

To be a commentator and participant in a claustrophic world is inevitably also to be commented upon. Type "Paul Bew" into an internet search engine and you encounter characterisations as bizarrely contrasting as "Marxist" and "mouthpiece for David Trimble".

As a teenager whose dislike of the political status quo paralleled a loathing of his philistine private school - "It was years before I could watch rugby without becoming physically angry," he says - Bew went on early civil rights marches. And as a professor in his early 50s, he has been a prominent supporter of David Trimble.

An ostensibly commonplace left-to-right progression conceals a vital consistency: sympathy for those trying to reconcile Ireland's two traditions. "While my language was more obviously leftwing in the 1970s than today, that sympathy has always been there," he says.

It doubtless helps that he has roots on both sides and, the hint of the ascetic in his appearance almost wholly misleading, lacks the deep-rooted religious allegiances that often underpin partisanship. He is generally described as a unionist. This is technically true. He says: "I support the principle of consent which is enshrined in the Good Friday agreement - and there is no likelihood of a majority in Northern Ireland choosing to leave the United Kingdom in the immediate future."

But he adds: "I don't write as a unionist." His publications include three sympathetic biographical studies of significant nationalist figures - Charles Stewart Parnell, John Redmond and Sean Lemass - and a highly critical study of the pre-1972 Northern Ireland state.

He rejects his frequent designation as an "adviser" to Trimble. "This is misleading because it does an injustice to the people who are employed as his advisers and also implies regular contact, whereas I sometimes go months without contact."

However, he accepts "informal adviser" as a reasonable description of a relationship that has grown from the late 1970s, when Trimble was a member of the interviewing panel that gave him his first job at Queen's. "There were two historians on the panel, but David was the only person who had read something I had recently written about Irish history, and asked a number of penetrating questions."

Bew confirms the general image of Trimble as a loner. "The title of his forthcoming memoirs, Himself Alone, is quite right." But he otherwise depicts a subtler, more complex figure than many would recognise. "As a young academic you expect universities to be full of people who are excited by books and talk about them, and you find out that most academics are not like that. David is one who was. He was one of the best people to talk to about any recent book on Irish history."

Seen in this light, his performance as Ulster Unionist leader is more easily explained. "Politicians who are clever, complex and well read always have a capacity for the unexpected. To win election he had to rely on rightwing support, so I didn't know if he would be able to move in the direction he has. I was certain once I heard that he had shown a draft copy of the conclusion of Between War and Peace [by Bew, Patterson and Paul Teague] to the prime minister, that he was serious about seeking an agreement."

Bew denies that political commit ment necessarily diminishes a historian, citing a long, distinguished line of Irish predecessors including Lecky, Froude, Stephen Gwynn and Conor Cruise O'Brien. "It hasn't stopped me pointing out when the agreement is in trouble, or where it has disappointed. It is clear, for instance, that it certainly has not brought about the era of good feeling that we hoped."

And he argues that closeness to the political process can aid a historian. He was at the Good Friday signing as a media commentator, and remembers: "We were told it was due to be signed at about 4am, went over and discovered instead that a new round of negotiations had started. Gerry Adams was outside phoning Clinton and there were advisers, journalists, academics and politicians all milling around together. I got a sense of the impact of sheer exhaustion on decision-making - settling that day rather than breaking to give participants a rest led to several weaknesses in the agreement - and also a greater awareness of the pressures on politicians. I won't again be easily sneery about politicians in the way that academics sometimes are."

He takes no satisfaction from the confirmation of his frequent observation that both traditions are increasingly polarised and inward-looking in the recent assembly elections. And he sees a possible, even likely, consequence as "a sort of political ice age which could last for years". Committed reconcilers would be marginalised and the demand for professing reduced, although he adds: "There'll always be a demand for objective analysis."

Bad news, as so often, for Northern Ireland - although Oxford University Press and connoisseurs of Irish history might be collateral beneficiaries.

Name Paul Anthony Bew

Age 54

Job Professor of Irish politics, Queen's, Belfast, since 1991

Before that degree and PhD in history, Pembroke College, Cambridge. Lecturer in history, Ulster Polytechnic. Queen's since 1979

Publications Ideology and the Irish Question 1912-1916; Between War and Peace (with Henry Patterson and Paul Teague);The Dynamics of Irish Politics (with Henry Patterson and Ellen Hazelkorn); The State in Northern Ireland 1921-72

Married to Greta Jones, professor of history, University of Ulster. One son.